The present invention relates to an interlocking device for a push-button switch used for the operation of cranes and hoists, for example. More specifically, it relates to an interlocking device of a push-button switch including a fixed contact on the switch body provided with two push buttons, having a mobile contact, which face each other. The push buttons being downwardly movable by pressing in multiple stages.
On a conventional push-button switch used for the operation of cranes and hoists, an interlocking member for the push button is swingably provided with approximately the middle position of two push buttons, provided face to face with each other in the proximity of the push-button switch. The interlocking member acts as a fulcrum, to prevent simultaneous pressing down of the two push buttons, so that the operator may not press down the two push buttons at the same time by mistake, causing reckless run or other trouble of the equipment. See U.S. Pat. No. 5,045,647.
Also, when the conventional interlocking device for a push-button switch is applied a push-button switch having a pair of push buttons facing each other and being downwardly movable by pressing in multiple stages, or in two stages for example, a problem was that to enable pressing down in two stages of either push button while preventing simultaneous pressing down of the two push buttons, it was impossible to maintain a large degree of freedom of a relative operating range between the two push buttons and the interlocking member due to the structure of this interlocking device. Thus it was difficult to maintain a sufficient stroke in each stage of the push buttons and, even when a sufficient stroke was maintained in each stage, a drop in the operability of the push buttons existed in both cases.